PROVENANCE, PALEOWEATHERING, AND TECTONIC CONTROLS ON THE LOWER-MIDDLE SIWALIK GROUP, KOHAT BASIN, PAKISTAN: SEDIMENTOLOGICAL AND GEOCHEMICAL CONSTRAINTS

This study integrates petrographic and geochemical analyses to constrain provenance, paleoweathering, and tectonic controls on sedimentation of the Lower–Middle Siwalik Group (Chinji, Nagri, and Dhok Pathan formations) in the Kohat Basin, western Himalayan foreland, northwest Pakistan. Provenance discrimination diagrams reveal an up-section shift from felsic granitic–gneissic sources of the Lesser and Higher Himalayas toward more quartzose detritus, reflecting progressive tectonic denudation related to early Main Central Thrust activity and enhanced sediment flux driven by southward propagation of the Main Boundary Thrust. Major-element weathering indices, A–CN–K systematics, and Th/U ratios indicate a systematic decrease in chemical weathering intensity up-section (CIA declining from approx.. 73 to approx. 66), attributed to accelerated uplift and erosion. Paleoclimatic proxies (Rb/Sr, Sr/Cu, C-value) suggest fluctuating semi-arid to semi-humid conditions with a trend toward warmer, drier climates in the upper succession. Paleoredox indicators confirm dominantly oxic conditions, whereas salinity proxies indicate freshwater to brackish depositional environments. Overall, the integrated dataset records a tectonically driven source-to-sink evolution characteristic of Himalayan foreland basin sedimentation.